“Fuel additives” are substances that can improve the fuel efficiency of an engine for example, as measured by the octane number, the cetane number or any other index suited to measure the efficiency of a particular fuel. A fuel additive also performs the function of lubricating, cleaning and stabilizing the fuel. Further, a fuel additive can also improve performance, economy, and injector life and reduce emissions and smoke related to an engine. A fuel additive can also help eliminate tank draining. A fuel additive can also possibly lower a gel point of the fuel in question. It can also provide a clean burning fuel that can inhibit polluting agents in emissions. These are a few examples of the functions of fuel additives and not a comprehensive or an exhaustive list. The compositions of the invention are intended for use as desirable fuel additives.
“Oxygenates” is a commonly referred to group of chemical compounds that raise the oxygen content of gasoline. Oxygen helps gasoline burn more completely, reducing harmful tailpipe emissions from motor vehicles. In one respect, the oxygen dilutes or displaces gasoline components such as aromatics (e.g., benzene), and sulfur. Additionally, it optimizes oxidation during combustion. Most gasoline suppliers meet the oxygen content requirements of the different clean fuel programs by adding oxygenate fuel additives, most commonly, methyl tertiary-butyl ether, (hereinafter referred to as MTBE) to gasoline blend stocks. Recently, various environmental protection agencies have begun raising concerns regarding the detection of MTBE in surface and ground water.
A need exists to develop esters with low water solubility that could be used to meet governmental oxygen requirements for gasoline and oxy-gasoline fuels. These low solubility esters would have a reduced solubility in surface and subsurface water and could therefore reduce the impact on such waters from spills and emissions of oxygenated fuels. It would also be desirable for MTBE replacements, including these esters, to have other favorable properties such as low ozone formation potential and a low rubber seal-swelling tendency.
The present invention relates to a gasoline fuel, diesel fuel or a biofuel comprising mixed esters as fuel additives, wherein the ester contains 2 to 22 carbon atoms. This invention also relates to a process of producing a mixture of levulinic acid esters and formic acid esters from biomass and olefins. It is believed that some of the compositions of esters of the invention have low water solubility. This invention further relates to using the compositions of esters as oxygenates in automotive gasoline used in internal combustion engines, as oxygenates in diesel engines, and as additives to biofuel. The invention also relates to the use of the esters as octane number-enhancing agents for gasoline, and as cetane number-enhancing agents in diesel fuels.
Levulinic acid is used to make resins, plasticizers, specialty chemicals, herbicides, and methyl tetrahydrofuran, which is used as a fuel extender, as a pharmaceutically active compound, and as a flavor substance. Levulinic acid is useful as a solvent, and as a starting material in the preparation of a variety of industrial and pharmaceutical compounds such as diphenolic acid (useful as a component of protective and decorative finishes), calcium levulinate (a particularly suitable form of calcium for intravenous injection used for calcium replenishment and for treating hypocalcemia, (see Cox et al., U.S. Pat. No. 2,033,909)). The use of the sodium salt of levulinic acid as a replacement for ethylene glycols as an antifreeze has also been proposed. Esters of levulinic acid are known to be useful as plasticizers and solvents, and have been suggested as fuel additives. Acid catalyzed dehydration of levulinic acid yields alpha-angelica lactone, which has been shown to increase octane ratings. Olson, E. S., et al., “Levulinate Esters from Biomass Wastes,” ACS Symposium Series, 784, 2001. Levulinic acid has been synthesized by a variety of chemical methods. But levulinic acid has not attained much commercial significance due in part to the high cost of the raw materials needed for synthesis. Another reason is the low yields of levulinic acid obtained from most synthetic methods. Yet, another reason is the formation of a formic acid byproduct during synthesis and its separation from the levulinic acid. Therefore, the production of levulinic acid has had high associated equipment costs. Despite the inherent problems in the production of levulinic acid, however, the reactive nature of levulinic acid makes it an ideal intermediate leading to the production of numerous useful derivatives.
Cellulose-based biomass, which is an inexpensive feedstock, is now used as a raw material for making levulinic acid. The supply of sugars from cellulose-containing plant biomass is immense and replenishable. Most plants contain cellulose in their cell walls. For example, cotton comprises 90% cellulose. Furthermore, it has been estimated that roughly 75% of the approximate 24 million tons of biomass generated on cultivated lands and grasslands are waste. The cellulose derived from plant biomass can be a suitable source of sugars to be used in the process of obtaining levulinic acid. Thus, the conversion of such waste material into a useful chemical, such as levulinic acid, would be desirable. Moreover, it would be most desirable to be able to produce levulinic acid in an economically viable and environmentally safe process. Levulinic acid production from biomass is briefly described in the processes of following U.S. patents.
U.S. Pat. No. 5,859,263 describes a process for producing levulinic acid by extrusion of mixture of starch, water and mineral acid in a screw extruder. Mineral acids that have been used are hydrochloric acid, hydrobromic acid, or sulfuric acid. The starch has an amylose content of 20–30%. The starch is obtained from corn, wheat, rice, tapioca, or mixtures thereof. The process is carried out in the temperature range of 80° C. to 150° C. Before the levulinic acid can be used for any of the purposes outlined above, it has to be separated out from the extrudate in a series of process steps. The separation is accomplished by partial neutralization, filtration/vacuum steam distillation, or solvent extraction. In a preferred embodiment, the extrudate is filter pressed, and the resulting filtrate is subjected to steam distillation. The discharge product of the distillation containing levulinic acid is condensed and centrifuged. Some, or all of the liquor discharged from the centrifugation is recycled to the preconditioning zones of a twin screw extruder.
U.S. Pat. No. 5,608,105 describes a process for producing levulinic acid by hydrolyzing a dilute concentration of carbohydrate-containing material in a mineral acid at temperatures in the range of 210° C. to 230° C. Hydroxymethylfurfural, along with other reaction intermediates are formed in this step. The products of this step are further hydrolyzed in presence of a mineral acid in the temperature range of 195–215° C. to give levulinic acid. This process gives levulinic acid in 60%–70% yield of the theoretical limit. Carbohydrate containing materials used for the process are waste paper sludge, raw wood flour, recycled paper sludge, wood paper sludge, and cellulose containing materials. In the second step, the process conditions are adjusted such that furfural and formic acid thus produced are vaporized and externally condensed. The levulinic acid settles at the bottom of the second reactor vessel. The conditions are adjusted such that any furfural and formic acid vaporize quickly.
U.S. Pat. No. 6,054,611 describes production of levulinic acid from sugars produced as a result of strong acid hydrolysis of biomass. The steps of this method include: 1) mixing biomass containing cellulose and hemicellulose with a solution of approximately 5–50% acid, preferably 10–30% acid, thereby decrystallizing the biomass, 2) heating the mixture to about 80–200° C., preferably 110–160° C., for 1 to 30 hours, preferably 2 to 10 hours, thereby hydrolyzing the cellulose and hemicellulose materials and causing the reaction of the resulting mixture of sugars to form the reaction products, 3) pressing or filtering to separating the liquid portions from the solid biomass portion, 4) separating the reaction products, and 5) recovering levulinic acid. It is preferred that the reaction products be filtered prior to separation. Additionally, it is preferable that the filter is washed one or two times and that preferably these washes are to be combined prior to separation. Moreover, following separation of the reaction products, levulinic acid can be concentrated to facilitate any further reaction.
As evident from the above-described methods, a major problem with using levulinic acid is the separation of pure levulinic acid from the byproducts, especially from formic acid. The present invention addresses the problem by describing a process which makes it unnecessary to separate out the formic acid, but instead produces a mixture of acid esters, which can be used as oxygenate additives to fuels, having superior oxygenate quality as compared to levulinic acid ester. Additionally, the ester formation process facilitates separation of the organic phase consisting of fuel additives from the aqueous phase.